The compounds of the present invention are described in the A. S. Tomcufcik et al. United States Letters Patents 3,725,407 issued Apr. 3, 1973; 3,828,041 issued Aug. 6, 1974 and 3,905,974 issued Sept. 16, 1975. The patentees describe methods for synthesizing 6-substituted 3-nitroimidazo[1,2-b]pyridazines and indicate that the compounds can be used to control amoebic and trichomonal infections in warm-blooded animals. No suggestion is made and it is not obvious from the disclosure that the stated compounds would be effective for the control of hemorrhagic colitis in swine.